The present invention relates to sheet feed members such as sheet feed rollers and sheet feed guides for feeding sheets from image forming devices such as copiers, facsimiles, laser beam printers (LBP) and other printers after forming images thereon in the image forming device.
Image forming devices that utilize electrophotographic process to form images, such as electrophotographic copiers and laser printers, transfer the images formed on photosensitive material onto transfer paper, fix the transferred images on the paper in an image fixing unit, and discharge the transfer paper.
Toner images transferred onto transfer paper are heat-fused and fixed to the transfer paper by passing the paper through a nip portion of the image fixing unit between an image-fixing roller with a built-in heater and a press roller pressed against the image-fixing roller in the image fixing unit. The paper is then discharged from the image former by paper discharge rollers.
FIG. 1 schematically shows a conventional image fixing unit of this type. It comprises an image-fixing roller 2 with a built-in heater 1 and a press roller 3 pressed against and rotated by the roller 2 with transfer paper sandwiched between the rollers 1 and 2. Transfer paper 5 fed from an unillustrated image transfer unit by a conveyor belt 4 and carrying unfixed toner images is inserted into a nip portion between the fixing roller 2 and the press roller 3 and fed therethrough. While being fed between the rollers 2 and 3, the toner images are fixed to the transfer paper. The paper 5 that has passed between the rollers 2 and 3 is separated from the fixing roller 2 by a stripping finger 7 provided downstream of the fixing roller 2.
The sheet 5 stripped from the fixing roller 2 passes through the feed path guided by sheet feeding slide guides 10, 11, passes between a paper discharge driven roller 9 and a paper discharge idler roller 8, and is discharged from the device while being guided by sheet feeding slide guides 12, 13.
In the case of the color laser printer shown in FIG. 2, transfer paper carrying unfixed toner images passes between an image-fixing roller 16 with a built-in heater and a pressure roller 17, is stripped from the fixing roller 16 by stripping fingers 18, passes between paper discharge rollers 19, 20, between a pair of intermediate guide rollers 21, and then between a drive roller 22 and a kicker roller 23, and is discharged from the device.
Other elements shown in FIG. 2 are a laser unit 30, a toner container 31, an unfixed-toner-image-forming drum 32, an image-transfer device 33, a paper (sheet) cassette 34 and an image-fixing device 35.
FIG. 3-5 show typical sheet feeding rolling elements used in image forming devices, such as paper discharge rollers, intermediate guide rollers and kicking rollers, of which the sheet feeding rolling element shown in FIG. 3 is used as a paper discharge roller or an intermediate roller. This roller has bosses 25 as rotary shafts at both ends of the roller body 24. The rolling element shown in FIG. 4, which is also used for similar purposes, has a shaft hole 26.
The sheet feeding rolling element shown in FIG. 5, which is used as a kicking roller, has geared bosses 28 at both ends of the roller body 27.
High flame resistance and heat resistance, as well as high followability to paper, are required for such sheet feed rollers as well as for paper discharge rollers. In order to meet these requirements, such materials as chloroprene rubber (CR) or polyacetal (POM) are widely used.
High flame resistance and heat resistance are also required for sheet feeding slide guides such as paper discharge guides, as are required for paper discharge rollers. High sliding properties are also required to smoothly pass paper sheets. Conventional slide guides are therefore made from e.g. polyphenylenesulfide (PPS) or polyacetal (POM).
One important requirement for today's copiers, LBP's, facsimiles, etc. is a shorter processing time. In order to shorten the processing time, it is necessary to increase the printing speed and thus the image fixing temperature (to about 250.degree. C.). The ambient temperature at the fixing unit of such a high-speed device is ordinarily 25-150.degree. C., but can reach to 50-250.degree. C.
Also, compactness of such image forming devices, especially copiers, is one of their prime selling points. In order to reduce the size of the entire device, the distance between the image fixing unit and the paper feed members such as feed rollers, feed guides and slide members has to be as short as possible.
But by shortening the treating time, there arose new problems which were not observed in conventional image forming devices, i.e. soiling with toner of sheet feeding parts such as sheet feeding rolling elements and sheet feeding slide guides, and heat deformation thereof.
Further, idler rolling elements having bosses or shaft holes tend to be deformed due to slide wear at their boss portions and shaft holes. Also, the mounting portion of the housing tends to be worn.
In particular, rolling elements with bosses tend to suffer deformation at their bosses due to pressure from other rollers and atmospheric temperature and friction heat during use.
If the slide guides are soiled with toner, images will be soiled or become unclear.
An object of this invention is to solve these problems and to provide sheet feeding parts for use in an image forming device, such as sheet feeding rolling elements or sheet feeding slide guides, which are high in heat resistance and wear resistance and to which toner is less likely to adhere.